The invention relates to low cost, automatic digitizers and methods for rapidly digitizing documents, and particularly to devices and methods utilizing multiple video cameras to achieve rapid automatic digitizing of large documents that extend beyond the field of view of a single video camera.
Various types of digitizers, including manual digitizers, are well known. Manual digitizers are widely used for low cost digitizing applications. Manual digitizers are those that require manual control of the positioning of a cursor or electronic pen or the like on a digitizing surface adjacent to a desired point of a document. Manual digitizers convert the coordinates of the desired point to digital numbers, either in response to a "digitize command" or continuously, as an electronic pen or cursor is positioned at a point of, or is removed along a line of, the document. Manual digitizers require the full-time attention of an operator to position the electronic pen or cursor. The accuracy of various types of manual digitizers usually is very sensitive to the presence of metallic or magnetic substances on or near the digitizing surface of the document to be digitized, to thermal expansion of substances in which grid conductors of a digitizing surface are embedded, and to the amount of tilt of the electronic pen. Manual digitizers are quite slow, due to the necessity of manually moving the cursor. For example, using a typical manual digitizer, a skilled operator may require approximately eight hours to digitize a 40-inch by 60-inch document, 20 percent of the area of which is covered by lines that are to be digitized.
Some present automatic digitizers, i.e., those that do not require an operator to position a cursor or electronic pen for each point or line digitized, use a video camera to scan a document area within the field of view of the video camera. Such automatic digitizing devices are extremely expensive, and their utilization has been limited to applications in which there has been crucial need for high speed digitizing of entire documents, such as satellite weather photos, medical X-ray photos, and the like. The high cost of automatic digitizers has been due to the fact that high resolution state-of-the-art video cameras are very expensive and a great deal of high speed data processing capability and memory storage capability is required to achieve automatic digitizing with high resolution. The required level of data processing capability and speed has been roughly equal to that of, for example, a PDP11 minicomputer made by Digital Equipment Corporation, or equivalent machines. Due to the high cost of automatic digitizing machines, they have not been developed for competition in the markets presently dominated by manual digitizers. Another reason, in addition to their high cost, that automatic digitizers have not been able to compete in the marketplace with manual digitizers is that "smart" manual digitizers are readily available at substantially lower cost. "Smart" digitizers are those that can "interface" with computers to provide "menu selection" of complex stored shapes (such as alpha-numerics) that can be almost instantly selected from a "menu" by appropriate positioning of a cursor or electronic pen and keyboard entry of commands calling up a selected shape that is stored in digitized form in the computer, although such stored shapes would be very time-consuming to digitize by manual positioning of a cursor or electronic pen. The availability of smart digitizers with this type of menu selection capability, and the exceedingly high cost of automatic digitizers, has caused it impractical to attempt to develop low cost automatic digitizing machines that would compete "head on" in the markets with manual digitizers. Furthermore, the limited field of view of the state-of-the-art video cameras and the need for certain minimum levels of resolution has led to the requirement that video cameras of present automatic digitizing devices be located relatively close to the document surface, preventing digitizing of large documents.
However, if automatic digitizers could be constructed inexpensively, the fact that they are capable of automatic operation without the cost of a human operator, the fact that they are extremely fast, and the fact that they are capable of digitizing not only point and line coordinates, but also degrees of darkness, suggest that automatic digitizers would be readily accepted if they could be provided inexpensively and with the capability of providing satisfactory resolution while digitizing large documents (as large or larger than the sizes that can be digitized by presently available manual digitizers).
Accordingly, it is an object of this invention to provide an automatic digitizing machine and method capable of high speed, accurate, high resolution automatic digitizing of position coordinates of points of large documents or items, at a cost that is competitive with the costs of presently known manual digitizers.
It is another object of the invention to provide a digitizing device and method that allows rapid, accurate digitizing of large documents utilizing a plurality of video cameras or other array type image sensor devices.